1 Technical Field of the Invention
The present invention relates to stators for electric rotating machines that are used in, for example, motor vehicles as electric motors and electric generators. In addition, the invention can also be applied to industrial machines and household electrical appliances.
2 Description of the Related Art
There are known stators for automotive electric rotating machines which include a stator coil formed by welding end portions of electric conductor segments.
Moreover, there are also known methods of reducing the heat input during the welding of the end portions, such as those disclosed in Japanese Patents No. 3303854 and No. 3964116.
Specifically, according to the method disclosed in Japanese Patent No. 3303854, each of the end portions of the electric conductor segments is stepped, as shown in FIG. 9, so as to have a reduced, constant cross-sectional area.
However, in the above case, during operation of the automotive electric rotating machine, in which the machine is subject to vibrations caused by running of the vehicle, or during the welding of the end portions of the electric conductor segments, in which each corresponding pair of the end portions are brought into contact with each other, stress concentration may occur at those parts of the end portions where the cross-sectional area is abruptly reduced. As a result, welds formed between the electric conductor segments may be easily broken.
On the other hand, according to the method disclosed in Japanese Patent No. 3964116, each of the end portions of the electric conductor segments includes, as shown in FIG. 10, a narrowing part in which the cross-sectional area of the end portion is continuously decreased toward the distal end of the end portion.
However, with the above method, if the decreasing rate of cross-sectional area of the narrowing part is set small, the length of the narrowing part will be large. As a result, the overall axial length of the stator coil will be accordingly increased, thereby making it difficult to minimize the size of the stator. In contrast, if the decreasing rate of cross-sectional area of the narrowing part is set large, the effect of reducing the heat input during the welding of the end portions of the electric conductor segments will be small. In other words, it is difficult to effectively reduce the heat input during the welding of the end portions.